A solder printer, a component mounting machine, a reflow furnace, a board inspection machine, and the like are examples of equipment which manufacture a printed circuit board onto which multiple electronic components are mounted. Such equipment is generally connected by board conveyance devices to construct a board production line. In the component mounting machine or the board inspection machine, a feeding screw drive device has been used from the related art as a drive device of a mounting head or a testing head. In recent years, demand for high speed movement and high precision positional control of a head has increased, and a linear motor is used as the drive device. A linear motor is not limited to use in component mounting machines and board inspection machines, and is widely used in various industrial machines which include linear motion capable sections.
In such a type of linear motor, it is understood that the positional dependency of the thrust constant which is a detail of the motor characteristics influences the control characteristics. The thrust constant is an index representing the occurrence rate of thrust in relation to the current which is supplied to the coil, and is represented by the unit N/A (Newtons/Amperes). For example, in a certain linear motor control system, when the thrust constant drops by approximately 10% depending on the position of the moving body on the track member, it is confirmed that the required time until the moving body reaches the target position is lengthened by approximately 10 ms during the movement control.
Individual differences in strength and size of each magnet, variation in the arrangement positions of the magnets which are lined up, and the like are conceivable as change factors with which the thrust constant changes depending on the position. It is possible to reduce the influence of the change factors by decreasing tolerances in component management and assembly work management in the manufacturing process. However, decreasing tolerances of the management links directly to the demerit of an increase in costs. In such a situation, a technique is generally used in which the change amount of the thrust constant is derived based on actual measurement, the control parameters are adjusted variably during the movement control, and the control performance is improved. Examples of techniques which derive the thrust constant based on actual measurement and use the thrust constant in the movement control are disclosed in PTLs 1 to 4.
A multi-phase linear motor drive device of claim 1 of PTL 1 is provided with a table referencing means which includes a reference table in which thrust change information at each position of a movable element (a moving body) is stored, and which sequentially references the reference table during driving. In claim 2 of PTL 1, a mode is disclosed in which a linear motor is driven at a substantially fixed velocity and a reference table is created based on a time series of state amounts which are obtained at this time. Accordingly, it is possible to drive the linear motor while sequentially referencing thrust change information at each position in the drive direction, and drive control which is stable and has sufficiently reduced control deviation is performed.
The techniques of PTLs 2 to 4 have commonality in that thrust ripple is expressed by a Fourier series. A thrust ripple measurement device of a linear motor of PTL 2 is configured to include a phase calculator which calculates the phase of the Fourier fundamental frequency based on the position of the linear motor, and a parameter determining device which determines ripple parameters based on the phase and a thrust instruction. Accordingly, by controlling the linear motor to move at a fixed velocity and calculating the ripple parameters based on the thrust instruction and the position of the linear motor, it is possible to measure the thrust ripple with high precision. A thrust ripple compensation device of PTL 3 and PTL 4 discloses a device which performs movement control using the thrust ripple which is measured in PTL 2.